Antihypertensive chroman derivatives

ABSTRACT

Compounds of formula (I) ##STR1## wherein: either one of R 1  and R 2  is hydrogen and the other is selected from the class of C 1-6  alkylcarbonyl, C 1-6  alkoxycarbonyl, C 1-6  alkylcarbonyloxy, C 1-6  alkylhydroxymethyl, nitro, cyano, chloro, trifluoromethyl, C 1-6  alkylsulphinyl, C 1-6  alkylsulphonyl, C 1-6  alkoxysulphinyl, C 1-6  alkoxysulphonyl, C 1-6  alkylcarbonylamino, C 1-6  alkoxycarbonylamino, C 1-6  alkylthiocarbonyl, C 1-6  alkoxythiocarbonyl, C 1-6  alkylthiocarbonyloxy, C 1-6  alkylthiolmethyl, formyl or aminosulphinyl, aminosulphonyl or aminocarbonyl, the amino moiety being optionally substituted by one or two C 1-6  alkyl groups, or C 1-6  alkylsulphinylamino, C 1-6  alkylsulphonylamino C 1-6  alkoxysulphinylamino or C 1-6  alkoxysulphonylamino or ethylenyl terminally substituted by C 1-6  alkylcarbonyl, nitro or cyano, or --C(C 1-6  alkyl)NOH or --C(C 1-6  alkyl)NNH 2 , or one of R 1  and R 2  is nitro, cyano or C 1-3  alkylcarbonyl and the other is methoxy or amino optionally substituted by one or two C 1-6  alkyl or by C 2-7  alkanoyl; 
     one of R 3  and R 4  is hydrogen or C 1-4  alkyl and the other is C 1-4  alkyl or R 3  and R 4  together with the carbon atom to which they are attached are C 2-5  polymethylene; 
     R 6  is hydrogen or C 1-6  alkyl; 
     R 7  is hydrogen or C 1-6  alkyl optionally substituted by hydroxy, C 1-6  alkoxy, C 1-6  alkoxycarbonyl or carboxy, or C 1-2  alkyl substituted by halogen, or C 2-6  alkenyl; 
     X is oxygen or sulphur; or, when one or the other of R 1  and R 2  is an amino or an amino-containing group, a pharmaceutically acceptable salt thereof, processes for their preparation and their use in the treatment of hypertension.

The present invention relates to novel chromans having pharmacological activity, to a process for preparing them, to pharmaceutical compositions containing them, and to their use in the treatment of mammals.

U.S. Pat. Nos. 4,110,347 and 4,119,643 and 4,251,537 and European Patent Publications Nos. 28 064 and 28 449 disclose classes of chromans that are described as having blood pressure lowering activity or anti-hypertensive activity.

A further class of chromans, has now been discovered which have been found to have blood pressure lowering activity.

Accordingly, the present invention provides a compound of formula (I): ##STR2## wherein:

either one of R₁ and R₂ is hydrogen and the other is selected from the class of C₁₋₆ alkylcarbonyl, C₁₋₆ alkoxycarbonyl, C₁₋₆ alkylcarbonyloxy, C₁₋₆ alkylhydroxymethyl, nitro, cyano, chloro, trifluoromethyl, C₁₋₆ alkylsulphinyl, C₁₋₆ alkylsulphonyl, C₁₋₆ alkoxysulphinyl,C₁₋₆ alkoxysulphonyl, C₁₋₆ alkylcarbonylamino, C₁₋₆ alkoxycarbonylamino, C₁₋₆ alkylthiocarbonyl, C₁₋₆ alkoxythiocarbonyl, C₁₋₆ alkylthiocarbonyloxy, C₁₋₆ alkylthiolmethyl, formyl or aminosulphinyl, aminosulphonyl or aminocarbonyl, the amino moiety being optionally substituted by one or two C₁₋₆ alkyl groups, or C₁₋₆ alkylsulphinylamino, C₁₋₆ alkylsulphonylamino C₁₋₆ alkoxysulphinylamino or C₁₋₆ alkoxysulphonylamino or ethylenyl terminally substituted by C₁₋₆ alkylcarbonyl, nitro or cyano, or --C(C₁₋₆ alkyl)NOH or --C(C₁₋₆ alkyl)NNH₂, or one of R₁ and R₂ is nitro, cyano or C₁₋₃ alkylcarbonyl and the other is methoxy or amino optionally substituted by one or two C₁₋₆ alkyl or by C₂₋₇ alkanoyl; one of R₃ and R₄ is hydrogen or C₁₋₄ alkyl and the other is C₁₋₄ alkyl or R₃ and R₄ together with the carbon atom to which they are attached are C₂₋₅ polymethylene;

R₆ is hydrogen or C₁₋₆ alkyl;

R₇ is hydrogen or C₁₋₆ alkyl optionally substituted by hydroxy, C₁₋₆ alkoxy, C₁₋₆ alkoxycarbonyl or carboxy, or C₁₋₂ alkyl substituted by halogen, or C₂₋₆ alkenyl;

X is oxygen or sulphur; or, when one or the other of R₁ and R₂ is an amino or an amino-containing group, a pharmaceutically acceptable salt thereof.

When one of R₁ and R₂ is hydrogen, the other is preferably selected from the class of C₁₋₆ alkylcarbonyl, C₁₋₆ alkoxycarbonyl, C₁₋₆ alkylcarbonyloxy, C₁₋₆ alkylhydroxymethyl, nitro or cyano. In particular, when one of R₁ and R₂ is hydrogen, the other is preferably nitro or cyano.

When one of R₁ and R₂ is hydrogen, it is preferred that R₂ is hydrogen.

When one of R₁ and R₂ is nitro, cyano or C₁₋₃ alkylcarbonyl the other is preferably amino optionally substituted by one or two C₁₋₆ alkyl or by C₂₋₇ alkanoyl. In particular, when one of R₁ and R₂ is nitro, cyano or C₁₋₃ alkylcarbonyl, the other is amino, methylamino, diethylamino or acetylamino. Most preferably, one of R₁ and R₂ is nitro or cyano, especially cyano, and the other is amino.

When one of R₁ and R₂ is nitro, cyano or C₁₋₃ alkylcarbonyl, it is preferred that R₁ is nitro, cyano or C₁₋₃ alkylcarbonyl.

The alkyl groups or alkyl moieties of alkyl-containing groups for R₁ or R₂ are, preferably, methyl or ethyl.

Preferably, R₃ and R₄ are both C₁₋₄ alkyl. In particular, they are both methyl or ethyl, preferably both methyl.

Examples of R₆ include hydrogen, methyl, ethyl, n- or iso-propyl. Preferably, R₆ is hydrogen or methyl, especially hydrogen.

Examples of R₇, when C₁₋₆ alkyl, include methyl,ethyl and n- and iso-propyl. Preferably R₇, when C₁₋₆ alkyl, is methyl.

Examples of R₇, when C₁₋₆ alkyl substituted by hydroxy, include methyl or ethyl terminally substituted by hydroxy.

A sub-class of R₇, when C₁₋₆ alkyl substituted by C₁₋₆ alkoxy, is C₁₋₆ alkyl substituted by methoxy or ethoxy. Examples thereof include methyl or ethyl terminally substituted by methoxy or ethoxy.

A sub-class of R₇, when C₁₋₆ alkyl substituted by C₁₋₆ alkoxycarbonyl, is C₁₋₆ alkyl substituted by methoxycarbonyl or ethoxycarbonyl. Examples thereof include methyl or ethyl terminally substituted by methoxycarbonyl or ethoxycarboxy.

Examples of R₇, when C₁₋₆ alkyl substituted by carboxy, include methyl or ethyl terminally substituted by carboxy.

A sub-class of R₇, when C₁₋₂ alkyl substituted by halogen, is methyl or ethyl terminally substituted by chloro or bromo, in particular by chloro.

Examples of R₇, when C₂₋₆ alkenoyl, include vinyl, prop-1-enyl, prop-2-enyl, 1-methylinyl, but-1-enyl, but-2-enyl, but-3-enyl, 1-methylenepropyl, or 1-methylprop-2-enyl, in both their E and Z forms where stereoisomerism exists.

Examples of a pharmaceutically acceptable salt of a compound of formula (I), when one or the other of R₁ and R₂ is an amino or an amino-containing group, include the hydrochloride and hydrobromide salts.

The present invention also provides a process for preparing a compound of formula (I), which comprises acylating a compound of formula (II): ##STR3## wherein R₁ ' and R₂ ' are R₁ and R₂, as hereinbefore defined, or a group or atom convertible thereto, R₃, R₄ and R₆ are as hereinbefore defined; Y and Z are both hydrogen or together form a bond with an acylating agent of formula (III):

    R.sub.7 --CO--L.sub.1                                      (III)

wherein R₇ is as hereinbefore defined and L₁ is a leaving group; and thereafter in the case where R₁ ' or R₂ ' is a group or atom convertible into R₁ or R₂, converting the group or atom into R₁ or R₂ ; optionally converting R₁ or R₂ in the resulting compound into another R₁ or R₂ ; in the case where X and Y together form a bond, reducing the Y-Z; bond optionally thiating the R₆ --N--CO--R₇ group in the resulting compound of formula (I) to give another compound of formula (I) wherein X is sulphur; and, when one or the other of R₁ and R₂ in the resulting compound of formula (I) is amino or an amino-containing group, optionally forming a pharmaceutically acceptable salt.

The leaving group (L₁) is a group that is displaceable by a primary or secondary amino nucleophile. Examples of such a group include C₂₋₉ acyloxy, such as mesyloxy, tosyloxy, triflate and C₁₋₄ alkylcarbonyloxy, and halogen, such as chloro and bromo. When the leaving group (L₁) is either of these examples, the acylating agent of formula (III) is either an acid anhydride or an acid halide. When it is acid anhydride, it may be a mixed or simple anhydride. If it is a mixed anhydride, it may be prepared in situ from a carboxylic acid and an acid halide.

When the acylating agent of formula (III) is an acid anhydride, the acylation of the compound of formula (II) is, preferably, carried out using the anhydride as the solvent in the presence of an acid acceptor, such as sodium acetate.

When the acylating agent of formula (III) is an acid halide, the acylation of the compound of formula (II) is, preferably, carried out in an aqueous medium, such as chloroform/water, in the presence of an acid acceptor, such as triethylamine, trimethylamine, pyridine, picoline or calcium, potassium or sodium carbonate.

Conversions of an aromatic group into R₁ or R₂, as hereinbefore defined, are generally known in the art of aromatic chemistry. For example, it is preferred when carrying out the acylation of a compound of formula (II), first to protect any unsubstituted terminal amine, that may be present for R₁ or R₂, such as amino aminosulphinyl, aminosulphonyl or aminocarbonyl, and afterwards to convert the protected amino moiety into the required terminal amine. Examples of protecting agents include acyl groups, such as acetyl, which may be added and removed conventionally. If it is desired to protect a terminal amino moiety in the presence of a cyano group then a more appropriate method is to use a trifluoroacetyl protecting group which may be removed by mild hydrolysis or to use a benzyloxycarbonyl or a p-nitrobenzyloxycarbonyl protecting group which may be removed by mild catalytic hydrogenolysis.

If the optional thiation reaction is to be carried out in order to obtain a compound of formula (I), wherein one or the other of R₁ and R₂ is a carbonyl-containing group and X is sulphur, it is preferred to use in the acylation reaction the corresponding compound of formula (II), wherein R₁ ' or R₂ ' is a protected carbonyl-containing group, and after thiation to convert the protected carbonyl-containing group into the required carbonyl-containing group for R₁ or R₂. Without such protection, the additional carbonyl group may give rise to a competing side-reaction. Examples of preferred carbonyl protecting groups include ketalising agents, which may be added and removed in conventional manner.

Examples of an optional conversion of R₁ or R₂ in the resulting compound of formula (I) into another R₁ or R₂, as defined hereinbefore, include the optional conversion of an α-hydroxethyl group into acetyl by oxidation, the optional conversion of a chloro atom into an amino group by amination, the optional conversion of an amino group into an amino group substituted by one or two C₁₋₆ alkyl or by C₂₋₇ alkanoyl, or the optional conversion of a hydrogen atom into a nitro group by nitration.

The reduction of a Y-Z bond may be carried out by conventional catalytic hydrogenation using Palladium on Charcoal.

The optional thiation of the R₆ --N--CO--R₇ group in a compound of formula (I) to give another compound of formula I, wherein X is sulphur, is, preferably, carried out with conventional thiation agents, such as hydrogen sulphide, phosporous pentasulphide and Lawesson's reagent (p-methoxyphenylthiophosphine sulphide dimer). The use of hydrogen sulphide and phosporous pentasulphide may lead to side-reactions and, therefore, the use of Lawesson's reagent is preferred.

The thiation reaction conditions are conventional for the thiation agent employed. For example, the use of hydrogen sulphide is, preferably, acid catalysed by, for example, hydrogen chloride in a polar solvent, such as acetic acid or ethanol. The preferred use of Lawesson's reagent is preferably carried out under reflux in a dry solvent, such as toluene or methylene chloride.

The optional formation of a pharmaceutically acceptable salt, when one or the other of R₁ and R₂ in the resulting compound of formula (I) is amino or an amino-containing group, may be carried out conventionally.

It will be appreciated that the invention further provides a process for the preparation of a compound of formula (I) which process comprises the reduction of a compound of formula (IV): ##STR4## wherein the variable groups are as hereinbefore defined; and thereafter in the case when R₁ ' or R₂ ' is a group or atom convertible into R₁ or R₂, converting the group or atom into R₁ or R₂ ; optionally converting R₁ or R₂ in the resulting compound of formula (I) into another R₁ or R₂ ; optionally thiating an R₆ NHCXR₇ group wherein X is oxygen to give a corresponding compound of formula (I) wherein X is oxygen; and, when R₁ and/or R₂ is amino or an amino containing group, optionally forming a pharmaceutically acceptable salt.

Compounds of formula (II) wherein Y and Z are both hydrogen may be prepared by reduction of compounds of formula (I) wherein Y and Z form a bond.

Compounds of formula (II) wherein Y and Z form a bond may be prepared by the dehydration of a compound of formula (V): ##STR5## wherein the R₆ NH and OH moieties are trans.

The dehydration may be carried out in accordance with conventional dehydration procedures, for example using a dehydrating agent, for example sodium hydride in an inert solvent, for example dry tetrahydrofuran at reflux temperatures.

A compound of formula (V) may be prepared by reacting a compound of formula (VI): ##STR6## wherein R₁ ', R₂ ', R₃ and R₄ are as hereinbefore defined, with a compound of formula (VII):

    R.sub.6 NH.sub.2                                           (VII)

or a salt thereof, wherein R₆ is as hereinbefore defined.

The reaction is normally carried out in a solvent, such as a C₁₋₄ alcohol, in particular methanol, ethanol or propanol at an ambient or an elevated temperature, for example 12° to 100° C. The reaction proceeds particularly smoothly if carried out in ethanol under reflux.

The resulting compound of formula (V) may be removed from the reaction mixture by removal of the solvent, for example, by evaporation under reduced pressure. Any epoxide impurity may be removed conventionally, for example by chromatography.

A compound of formula (VI) may be prepared, preferably in situ, by reacting a compound of formula (VIII): ##STR7## wherein R₁ ', R₂ ', R₃ and R₄ are as hereinbefore defined and the hydroxy group is trans to the bromo atom, with a base, such as potassium hydroxide, in a solvent, such as ether or aqueous dioxan.

Compounds of formula (VIII) are known and may be prepared in accordance with any appropriate known process, for example, by the process described in the aformentioned U.S. patents and European patent publications. Schematically, such process can be depicted thus. ##STR8## (a) Room temperature; NaOH/40% benzyltrimethylammonium hydroxide in methanol;

(b) Heat in o-dichlorobenzene;

(c) N-bromosuccinimide/dimethylsulphoxide/water;

(d) Bromine in carbon tetrachloride; and

(e) Acetone/water.

The above process may produce mixtures of compounds during reaction (b) owing to the two sites available for ring formation. It is therefore advisable to remove any of the undesired compound by, for example, chromatography, before reaction (c) or (d).

As mentioned previously, the compounds of formula (I) exist in optically active forms, and the processes of the present invention produce mixtures of such forms. The individual isomers may be separated one from the other by chromatography using a chiral phase.

The compounds of formula (III) and (VII) are also known or can be prepared analogously to the preparation of known compounds.

A number of the compounds of formula (II) are known from the aforementioned U.S. Patents and European Patent publications. However, there is a novel class of compounds falling ithin formula (II) which are of formula (IX): ##STR9## wherein either one of R₁ " and R₂ " is hydrogen and the other is C₁₋₆ alkylcarbonyl, C₁₋₆ alkoxycarbonyl, C₁₋₆ alkylcarbonyloxy, C₁₋₆ alkylhydroxymethyl or cyanoor one of R₁ " and R₂ " is C₁₋₆ alkylcarbonyl, nitro or cyano and the other is amino and R₈ " is methyl or ethyl.

A preferred sub-class of compounds of formula (IX) are those wherein the alkyl groups or alkyl moieties of alkyl-containing groups are methyl or ethyl.

The compounds of formula (IX) are particularly useful intermediates, which can be prepared as hereinbefore described and which represent part of the present invention.

As mentioned previously, the compounds of formula (I) have been found to have blood-pressure lowering activity. They are therefore useful in the treatment of hypertension.

The present invention accordingly provides a pharmaceutical composition which comprises a compound of the formula (I) or a pharmaceutically acceptable salt thereof and a pharmaceutically acceptable carrier. In particular, the present invention provides an anti-hypertensive pharmaceutical composition which comprises an anti-hypertensive effective amount of a compound of the formula (I) and a pharmaceutically acceptable carrier.

The compositions are preferably adapted for oral administration. However, they may be adapted for other modes of administration, for example parenteral administration for patients suffering from heart failure.

In order to obtain consistency of administration it is preferred that a composition of the invention is in the form of a unit-dose. Suitable unit dose forms include tablets, capsules and powders in sachets or vials. Such unit dose forms may contain from 1 to 100 mg of a compound of the invention and more usually from 2 to 50 mg, for example 5 to 25 mg such as 6, 10, 15 or 20 mg. Such compositions may be administered from 1 to 6 times a day, more usually from 2 to 4 times a day, in a manner such that the daily dose is from 5 to 200 mg for a 70 kg human adult and more particularly from 10 to 100 mg.

The compositions of the invention may be formulated with conventional excipients, such as a filler, a disintegrating agent, a binder, a lubricant, a flavouring agent and the like. They are formulated in conventional manner, for example in a manner similar to that used for known anti-hypertensive agents, diuretics and β-blocking agents.

The present invention further provides a compound of the formula (I) for use in the treatment of hypertension.

The present invention yet further provides a method of treating hypertension in mammals including man, which comprises administering to the suffering mammal an anti-hypertensive effective amount of a compound of formula (I) or a pharmaceutically acceptable salt thereof or a pharmaceutical composition of the invention.

The following descriptions relate to the preparation of intermediates and the following example relates to the preparation of a compound of formula (I).

Description 1 Trans-4-N-acetylamino-6-cyano-3,4-dihydro-2,2-dimethyl-2H-benzo[b]pyran-3-ol ##STR10##

6-Cyano-3,4-dihydro-2,2-dimethyl-3,4-epoxy-2H-benzo[b]pyran (10.0 g) was stirred in ethanol (20 ml) and the ammonium hydroxide solution (50 ml) for 4 days at room temperature. Evaporation gave a yellow gum (10.1 g) which solidified on standing.

This solid (1.0 g), anhydrous sodium acetate (2.00 g) and acetic anhydride (20 ml) were stirred for 5 hours at room temperature. The mixture was poured into water and extracted with ethyl acetate. This was washed with water and brine, and dried over MgSO₂. Removal of drying agent, and evaporation gave a solid which was chromatographed using a chromaton (2 mm silica gel HF₂₅ plate, solvent flow 6 ml/min elution with ethyl acetate-pentane using a gradient technique gave a fraction which contained the crude title compound. Recrystallisation of this material from ethyl acetate gave trans-4-N-acetylamino-6-cyano-3,4-dihydro-2,2-dimethyl-2H-benzo[b]pyran-3-ol (208 mgm) as crystals of m.p. 203-250.

NMR (CDCl₃ -DMSOd₆) 1.25 (3H,s), 1.47 (3H, s), 2.08 (3H, s), 3.60 (q, J=9, 5 Hz), 4.93 (q, J=9, 8 Hz), 5.24 (d, J=5 Hz), 6.86 (d, J=8 Hz), 7.43 (q, J=8, 2 Hz) overlapping 7.50 (d, J=2 Hz) 8.00 (d, J=8 Hz).

Anal. C₁₄ H₁₆ H₂ O₃ requires: C, 64.60; H, 6.20; N, 10.76. found: C, 64.51; H, 6.21; N, 10.78%.

Description 2 4-Acetylamino-6-cyano-2,2-dimethyl-2H-benzo[b]pyran ##STR11##

The compound of example 2, (0.5 g) and sodium hydride (0.058 g, 80% dispersion in oil) were heated under reflux in dry xylene (50 ml) in an atmosphere of nitrogen for 48 hours. After cooling, water (25 ml) was added cautiously, and the layers separated. The organic phase was washed with water and brine, and dried over anhydrous magnesium sulphate. Filtration and evaporation gave a gum which was chromatographed (chromatotron, gradient elution: ethyl acetate-pentane, 2 mm silica gel, 6 ml/min) to give the title compound (230 mg) in the initial fractions, as needles (65 mg) from diethyl ether, having a m.p. of 146°-147° C.

NMR (CDCl₃) 1.50 (6H, s); 2.23 (3H, s); 6.37 (1H, s); 6.90 (1H, d, J=9 Hz) overlapping 7.00 (1H, m); 7.45 (1H, q, J-9, 2 Hz) overlapping; 7.52 (1H, d, J=2 Hz).

EXAMPLE 1 4-Acetylamino-6-cyano-2,2-dimethyl-2H-1-benzopyran (compound 1) ##STR12##

4-Acetylamino-6-cyano-2,2-dimethyl-2H-1-benzopyran (180 mgm) and 10% Palladium/carbon (100 mg) in ethanol (25 ml) were shaken under hydrogen for 6 days at room temperature. Filtration and evaporation gave a brown gum (180 mgm) which was purified using a chromatotron, elution with ascending concentrations of ethyl acetate in pentane, giving a fraction which was recrystallised from ethyl acetate-hexane to give the title compound (25 mgm) of m.p. 166°-167° C.

Mass spectrum C₁₄ H₁₆ N₂ O₂ requires M⁺ at m/z 244.1212; found M⁺ at m/z 244.1216.

NMR (CDCl₃) δ 1.33 (3H, s); 1.46 (3H, s); 1.72 (1H, t, J=8, 8 Hz); 2.08 (3H, s); 2.19 (1H, q, J=8, 4 Hz); 5.27 (1H, m); 6.05 (1H, d, J=5 Hz); 6.82 (1H, d, J=11 Hz); 7.37 (1H, q, J-11, 2 Hz); 7.53 (1H, narrow m).

The following compounds are prepared analogously and from intermediates described in EP No. 95316 and allowed U.S. patent application No. 496,174:

    ______________________________________      ##STR13##     Ex No  R.sub.1   R.sub.2   R.sub.6                                      R.sub.7  X     ______________________________________     2      NC        H         C.sub.2 H.sub.5                                      CH.sub.3 O     3      NC        H         H     CHCH.sub.2                                               O     4      NC        H         CH.sub.3                                      CH.sub.3 O     5      NC        H         H     C.sub.2 H.sub.2                                               O     6      NC        H         H     (CH.sub.2).sub.3 CH.sub.3                                               O     7      Cl        H         H     CH.sub.3 O     8      CH.sub.3 CO                      H         H     CH.sub.3 O     9      CH.sub.3 CONH                      O.sub.2 N H     CH.sub.3 O     10     O.sub.2 N CH.sub.3 CONH                                H     CH.sub.3 O     11     NC        H         H     CH.sub.2 Cl                                               O     12     NC        H         H     CH.sub.2 COCH.sub.3                                               O     13     NC        H         H     CH.sub.3 S     14     NC        H         H     H        O     ______________________________________

Pharmacological Data

Systolic blood pressures were recorded by a modification of the tail cuff method described by I. M. Claxton, M. G. Palfreyman, R. H. Poyser, R. L. Whiting, European Journal of Pharmacology, 37, 179 (1976). A W+W BP recorder, model 8005, was used to display pulses prior to all measurements rats were placed in a heated environment (33.5°±0.5° C.) before transfer to a restraining cage. Each determination of blood pressure was the mean of at least 6 readings. Spontaneously hypertensive rats (ages 12-18 weeks) with systolic blood pressures >170 mmHg were considered hypertensive.

    ______________________________________                           % Change in     Compound of                Time Post  Systolic Blood                                       % Change in     Example    Dose Hours Blood       Heart Rate     ______________________________________     6 rats     1          -34 ± 6  2 ± 2     Dose 1 mg/kg                 2*        -31 ± 8  0 ± 3     p.o.     Initial Blood                4          -38 ± 4  4 ± 2     Pressure   6          -44 ± 7  -1 ± 2     202 ± 6 mmHg     Initial Heart                24          -8 ± 4  -6 ± 3     Rate     501 ± 10 beats/     min     ______________________________________      *At 2 hours 2 rats had no measurable pulse

Toxicity

No toxic effects were observed in the above test. 

I claim:
 1. A compound of the formula (I): ##STR14## wherein: R₁ is nitro, cyano, chloro, or acetyl and R₂ is hydrogen, or one of R₁ and R₂ is nitro, cyano or acetyl and the other is amino, methylamino, dimethylamino or acetylamino;R₃ and R₄ are both methyl; R₆ is hydrogen or C₁₋₆ alkyl; R₇ is hydrogen or C₁₋₆ alkyl optionally substituted by hydroxy, C₁₋₆ alkoxy, C₁₋₆ alkoxycarbonyl or carboxy, or C₁₋₂ alkyl substituted by halogen, or C₂₋₆ alkenyl; X is oxygen or sulphur; or when one or the other of R₁ and R₂ is an amino or an amino-containing group, a pharmaceutically acceptable salt thereof.
 2. A compound according to claim 1 wherein R₂ is hydrogen and R₁ is acetyl, nitro or cyano.
 3. A compound according to claim 2 wherein R₂ is hydrogen and R₁ is nitro or cyano.
 4. A compound according to claim 1, wherein R₆ is hydrogen.
 5. A compound according to claim 1, wherein R₇ is methyl.
 6. 4-Acetylamino-6-cyano-2,2-dimethyl-2H-1-benzopyran.
 7. A pharmaceutical composition for the treatment of hypertension, comprising an effective amount of a compound according to claim 1 or a pharmaceutically acceptable salt thereof and a pharmaceutically acceptable carrier.
 8. The composition according to claim 7, wherein said compound is 4-acetylamino-6-cyano-2,2-dimethy-2H-1-benzopyran.
 9. A method of treating hypertension in mammals including man, which comprises administering to the sufferer an anti-hypertensive amount of the compound according to claim 1 or a pharmaceutically acceptable salt thereof.
 10. The method according to claim 9, wherein said compound is 4-acetylamino-6-cyano-2,2-dimethyl-2H-1-benzopyran. 